One-pot enantioselective synthesis of (S)-spirobrassinin and non-natural (S)-methylspirobrassinin from amino acids using a turnip enzyme

The enantioselective synthesis of ( S )-(−)-spirobrassinin, which features a unique sulfur-containing spirooxindole skeleton, was achieved by focusing on the phytoalexin generation in Brassicaceae plants. Specifically, ( S )-(−)-spirobrassinin was obtained in a one-pot fashion from l -tryptophan through a reaction involving S -spirocyclization with various turnip enzymes and constituents, i.e., using the turnip as a reaction reagent, catalyst, and reaction vessel. Surprisingly, this strategy also enabled the one-pot enantioselective synthesis of the novel non-natural spirooxindole ( S )-(−)-5-methylspirobrassinin from 5-methyl- dl -tryptophan. Graphic abstract